1. Field of the Invention
The present invention relates to a digital watermark inserting system for inserting digital watermark information into an input image, a digital watermark characteristic parameter table generating method, and a computer readable record medium on which a digital watermark characteristic parameter table generating program has been recorded.
2. Description of the Related Art
In recent years, digital watermarks are becoming attractive. However, there have been few studies that focus on attacks against digital watermarks. As a result, it is difficult to compare robustness values against attacks in different digital watermark systems. As a related art reference, a framework of a robustness evaluation value calculating system for categorizing attacks that take place in conventional image processing and so forth and calculating robustness evaluation values for individually categorized attacks has been disclosed by Ryoma Oami, Yoshihiro Miyamoto, and Mutsumi Ohta, NEC C and C Media Research Laboratories in xe2x80x9cRobustness Measure against attacks for digital watermarking and its application,xe2x80x9d 1998 Image Media Processing Symposium (IMPS 98). The related art reference describes a method for obtaining the optimum digital watermark strength.
In the related art reference, attacks against digital watermarks are largely categorized as (1) deterioration that takes place in an image processing or the like and (2) intentional forgery of embedded information. Since attacks of the category (1) inevitably take place in a conventional image process. Thus, strong robustness is required for attacks of the category (1). Attacks of the category (2) are higher level attacks than those of the category (1). The attacks of the category (2) largely depend on the digital watermark inserting and detecting system. In the related art reference, attacks of the category (1) are further categorized from a view point of a signal processing. Robustness evaluation values are calculated for individually categorized attacks. The categorized attacks are for example coding loss in JPEG (LC), uniform and Gauss type noise (N), geometric transform such as scale and rotation (GT), pixel value conversion such as gray and binary (PVC), and image processing such as sharpening and median filtering (IP).
In the system of the related art reference, a digital watermark is inserted into an image. Thus, a digital watermark inserted image is obtained. Thereafter, the digital watermark inserted image is attacked in a predetermined manner and then the digital watermark is detected. By repeating the above procedures, varying a parameter for adjusting the attack strength, a detection ratio is obtained. The detection ratio data is statistically processed. Thus, robustness evaluation values for individually categorized attacks are calculated. As the statistical process, weighted means method or threshold value method is used, for example. In the evaluation value calculating system, (a) by properly setting a weighting function, evaluation values for applications having different attack characteristics can be calculated; (b) robustness evaluation values can be compared among different systems regardless of the values of the attack strength x for really measuring detection ratios; and (c) the accuracy of evaluation values can be improved progressively. According to the evaluation values calculating system, evaluation values 0 to 1 against watermark strength values 1 to 4 depend on conventional digital watermark systems.
However, according to the digital watermark inserting system of the related art reference, it is difficult to properly set the strength of a digital watermark. The strength of the digital watermark largely depends on the contents of the image. Even if the user designates the relation of the strength of digital watermarks, the deterioration of the image quality, and the robustness values against attacks in a deterministic manner, the relation cannot be applied to all images. Thus, the optimum strength of digital watermarks cannot be obtained.
The inventor of the present invention has invented xe2x80x9cdigital watermark inserting systemxe2x80x9d that is currently being filed as Japanese Patent Application No. 10-150823 (hereinafter, this invention may be referred to as second related art reference). This invention was made to embed (insert) copyright information and so forth into digital signals of audio data, image data, and so forth.
FIG. 1 is a block diagram showing the structure of the xe2x80x9cdigital watermark inserting systemxe2x80x9d as the second related art reference. In FIG. 1, a categorizing portion 103 calculates a feature amount of an input image, obtains a category of the image with the calculated feature amount, and outputs the index indicating the category as a category index to a storing unit 2001. The storing unit 2001 selects a table corresponding to the category index that is received from the categorizing portion 103 and outputs an image quality deterioration ratio and a robustness evaluation value corresponding to digital watermark strength that is received from a digital watermark strength calculating portion 100 to the digital watermark strength calculating portion 100.
The digital watermark strength calculating portion 100 outputs various digital watermark strength values to the storing unit 2001. The digital watermark strength calculating portion 100 decides the optimum digital watermark strength based on the image quality deterioration ratio and the robustness evaluation value that are received from the storing unit 2001 and based on restriction information of digital watermark strength that is input by the user and outputs the decided optimum digital watermark strength data to a digital watermark inserting portion 102.
The digital watermark inserting portion 102 converts embedding data into digital watermark information, inserts the digital watermark into the image with the optimum digital watermark strength received from the digital watermark strength calculating portion 100, and outputs a digital watermark inserted image.
Next, the operation of the digital watermark inserting system shown in FIG. 1 will be described. First of all, several symbols used in the operation will be defined.
The number of categories of input images is denoted by K. K categories are distinguished with category index k (where k=1, . . . , K). The digital watermark strength with which a digital watermark is inserted is denoted by s(m) (where m=1, . . . , M). The parameter used as the digital watermark strength depends on the digital watermark inserting algorithm for use. When the digital watermark strength is successively varied, it is digitized into M different values and their values are denoted by s(m). When the category index is k and the digital watermark strength is s(m), the image quality deterioration ratio and the robustness evaluation value against the attack are denoted by D(k,m) and V(k,m), respectively.
Next, with reference to FIG. 1, the operation of the digital watermark inserting system will be described. An input image is supplied to the categorizing portion 103. The categorizing portion 103 calculates a feature amount of the image, decides the category of the input image based on the obtained feature amount, and outputs a category index that represents the category. In reality, the categorizing portion 103 stores feature amount values that represent boundaries of categories. The categorizing portion 103 compares the stored feature amount values with the calculated feature amount value and categorizes the input image based on the compared result. The feature amount is for example an activity of the entire image (the activity is the mean value of AC frequency components).
The category index that is output from the categorizing portion 103 in input to the storing unit 2001. The storing unit 2001 stores digital watermark feature tables for individual category indexes. Each of the digital watermark feature tables represents the relation of the digital watermark strength values, the image quality deterioration ratios and the robustness evaluation values against attacks. A digital watermark characteristic table for a category index k is shown in Table 1.
In addition, when a digital watermark strength s(m) is input from the digital watermark strength calculating portion 100, the storing unit 2001 selects a digital watermark characteristic table corresponding to the category index k that is received from the categorizing portion 103, and outputs the image quality deterioration amount D(k, m) and the robustness evaluation value V(k, m) to the digital watermark strength calculating portion 100.
After the input image has been supplied to the system and the categorizing portion 103 has calculated the category index k, the digital watermark strength calculating portion 100 calculates the optimum digital watermark strength based on digital watermark strength restriction information that is input by the user. Basically, the digital watermark strength that maximizes the following objective function is defined as the optimum digital watermark strength.
Z(m)=(1xe2x88x92a)(1xe2x88x92D(k, m))+aV(k, m) xe2x80x83xe2x80x83(1) 
where a satisfies the relation of 0xe2x89xa6axe2x89xa61. Z(m) is calculated for each digital watermark strength value. The digital watermark strength s(m) with the maximum value is calculated as the optimum digital watermark strength.
The optimum digital watermark strength that is output from the digital watermark strength calculating portion 100 is input to the digital watermark inserting portion 102. The digital watermark inserting portion 102 converts the input embedding data into digital watermark information and inserts the input embedding data into the image. The digital watermark strength used in inserting the input embedding data into the image is the optimum digital watermark strength that is output from the digital watermark strength calculating portion 100. The resultant image is output as a digital watermark inserted image.
According to the second related art reference, the digital watermark inserting algorithm is not limited as long as the user can designate the digital watermark strength or the like for the digital watermark inserted into the image. For example, the watermarking algorithm disclosed in Japanese Patent Laid-Open Publication No. 9-191394 and periodical xe2x80x9cIEEE Transactions on Image Processing,xe2x80x9d Vol. IP-6, pp. 1673-1687, No. 12, 1997 can be used.
In this algorithm, the entire image is processed by discrete cosine transform (DCT) method or discrete Fourier transform (DFT) method. The N largest transform coefficients are selected from the obtained transform coefficients. Thereafter, digital watermark information is inserted. In reality, digital watermark information is inserted corresponding to the following formula.
xcexdxe2x80x2=xcexd+xcex1x xe2x80x83xe2x80x83(2) 
or
xcexdxe2x80x2=xcexd(1+xcex1x) xe2x80x83xe2x80x83(3) 
where x is a digital watermark signal; xcexd is a transform coefficient into which the watermark signal is embedded; xcex1 is the digital watermark strength; and xcexdxe2x80x2 is a digital watermark inserted transform coefficient. For the obtained digital watermark inserted transform coefficient, inverse DCT method or inverse DFT is performed. Thus, a digital watermark inserted image is generated and output. In this algorithm, the digital watermark strength is represented by parameter xcex1 in the formula (2) or the formula (3).
Next, a digital watermark characteristic table generating unit that generates a digital watermark characteristic table stored in the storing unit 2001 of the system shown in FIG. 1 will be described. FIG. 2 is a block diagram showing the structure of a conventional digital watermark characteristic table generating unit. In FIG. 2, a digital watermark inserting portion 200 converts embedding data into proper data, inserts digital watermark information with the input digital watermark strength into the input image, and outputs the resultant digital watermark inserted image to an attack executing portion 201. The attack executing portion 201 attacks the digital watermark inserted image with a predetermined strength corresponding to an input attack parameter in a predetermined manner and outputs the attacked image to a digital watermark detecting portion 202.
The digital watermark detecting portion 202 detects a digital watermark from the attacked image that is received from the attack executing portion 201 and outputs the detected result to a digital watermark characteristic table generating portion 2201. An image quality deterioration amount calculating portion 203 calculates an image quality deterioration amount with both the digital watermark inserted image that is received from the digital watermark inserting portion 200 and the input image and outputs the calculated image quality deterioration amount to the digital watermark characteristic table generating portion 2201. A categorizing portion 204 categorizes the input image and outputs a category index corresponding to the categorized result to the digital watermark characteristic table generating portion 2201.
The digital watermark characteristic table generating portion 2201 obtains a robustness evaluation value against the attack and an image quality deterioration ratio, based on the detected result that is received from the digital watermark detecting portion 202, the digital watermark strength, the attack parameter, the image quality deterioration amount that is received from the image quality deterioration amount calculating portion 203, and the category index that is received from the categorizing portion 204, and it outputs the relation of the robustness evaluation value, the image quality deterioration ratio, and the digital watermark strength as a digital watermark characteristic table.
Next, the operation of the digital watermark characteristic table generating unit shown in FIG. 2 will be described. For easy understanding, several symbols necessary for explaining the operation of the digital watermark characteristic table generating unit will be defined.
The number of input images is denoted by I. The I input images are distinguished by an index i (where i=1, . . . , I). The value of the attack parameter is denoted by x(j) (where j=1, . . . , J). The attack parameter is a parameter for adjusting the attack strength. The category index k (where k=1, . . . , K), the digital watermark strength s(m) (where m=1, . . . , M), the image quality deterioration ratio D(k, m), and the attack robustness evaluation value V(k, m) are defined as described above. A category index for an input image i is denoted by k(i). An image quality deterioration amount for an input image i is denoted by d(i). When the category index is denoted by k, the digital watermark strength index is denoted by m, and the attack parameter index is denoted by j, the detected result and the detection ratio are denoted by y(k, m, j) and r(k, m, j), respectively.
Next, with reference to FIG. 2, the operation of the digital watermark characteristic table generating unit will be described. An input image i is supplied to the digital watermark inserting portion 200. Input embedding data is converted into digital watermark information. With a parameter of input digital watermark strength s(m), the digital watermark is inserted into the image. The obtained image is output as a digital watermark inserted image to the image quality deterioration amount calculating portion 203 and the attack executing portion 201.
The attack executing portion 201 attacks the digital watermark inserted image in a predetermined manner and outputs the attacked image to the digital watermark detecting portion 202. The attack strength is adjusted by the input attack parameter x(j). When the digital watermark inserted image is attacked by a noise adding attack, the attack parameter is an amount of noise power, noise amplitude, PSNR (Peak Signal to Noise Ratio), or the like. When the digital watermark inserted image is attacked as an enlarging attack or a shrinking attack, the attack parameter is an amount of enlargement/shrinkage magnification or equivalent amount.
The attacked image that is output from the attack executing portion 201 is input to the digital watermark detecting portion 202. The digital watermark detecting portion 202 detects a digital watermark from the attacked image. When the digital watermark detecting portion 202 has detected an embedded digital watermark, it outputs xe2x80x9c1xe2x80x9d as a detected result. When the digital watermark detecting portion 202 has not detected an embedded digital watermark, it outputs xe2x80x9c0xe2x80x9d as a detected result. When the digital watermark detecting portion 202 has detected part of an embedded digital watermark, it outputs a value between xe2x80x9c0xe2x80x9d and xe2x80x9c1xe2x80x9d (for example, xe2x80x9c0.5xe2x80x9d) as a detected result. The data that is output from the digital watermark detecting portion 202 is input to the digital watermark characteristic table generating portion 2201.
Both the input image and the digital watermark inserted image that is output from the digital watermark inserting portion 200 are input to the image quality deterioration amount calculating portion 203. The image quality deterioration amount calculating portion 203 compares the input image with the digital watermark inserted image and calculates the image quality deterioration amount due to the inserted digital watermark. As the image quality deterioration amount, a PSNR value of the digital watermark inserted image against the original image or a WSNR (Weighted Signal to Noise Ratio) value in consideration of visual characteristics is used. Alternatively, a ratio of the deterioration to a JND (Just Noticeable Distortion), which is derived by dividing the differences between the digital watermark inserted image and the original input image by JND values after the JND values are calculated, can be used. The calculated image quality deterioration amount is output to the digital watermark characteristic table generating portion 2201.
In FIG. 2, the input image is also supplied to the categorizing portion 204. The operation of the categorizing portion 204 is the same as that of the categorizing portion 103 shown in FIG. 1. The categorizing portion 204 calculates a feature amount of the input image and categorizes the input image based on the calculated feature amount. Thereafter, the categorizing portion 204 outputs a category index that represents the category to the digital watermark characteristic table generating portion 2201.
The digital watermark characteristic table generating unit shown in FIG. 2 performs such a process for I input images i=1, . . . , I. For each input image i, the procedures described above are performed with the M different digital watermark strength values s(m) (where m=1, . . . , M). For each digital watermark strength s(m), the procedures described above are performed with the J different attack parameters x(j) (where j=1, . . . , J). The detected results y(k(i), m, j), the digital watermark strength s(m), the index m, the attack parameter x(j), the index j, the image quality deterioration amount d(k(i), m), and the category index k(i) are supplied to the digital watermark characteristic table generating portion 2201. The digital watermark characteristic table generating portion 2201 generates and outputs a digital watermark characteristic table describing the relation between these input factors.
Next, the digital watermark characteristic table generating portion 2201(2303) will be described. FIG. 3 is a block diagram showing the structure of the digital watermark characteristic table generating portion 2201(2303). A detected result totaling portion 300 totals the detected result of the digital watermark detecting portion 202 for each attack parameter, each digital watermark strength, and each category index, calculates a detection ratio with the totaled result, and outputs the calculated detection ratio to a robustness evaluation value calculating portion 2301.
An image quality deterioration amount totaling portion 301 totals the image quality deterioration amount that is received from the digital watermark deterioration amount calculating portion 203 for each category index and each digital watermark strength, calculates an image quality deterioration ratio with the totaled image quality deterioration amount, and outputs the calculated image quality deterioration ratio to a data combining portion 2302.
Next, a robustness evaluation value calculating portion 2301 calculates an attack robustness evaluation value with the attack parameter and the detection ratio that is received from the detected result totaling portion 300 and outputs the calculated attack robustness evaluation value to the data combining portion 2302. For each category index, the data combining portion 2302 generates a table that describes the relation between the digital watermark strength, the image quality deterioration ratio, and the robustness evaluation value, and outputs the table as a digital watermark characteristic table.
Next, the operation of the digital watermark characteristic table generating portion shown in FIG. 3 will be described. The digital watermark detected result y(k(i), m, j) is input to the detected result totaling portion 300. The detected result totaling portion 300 has a storing means. The detected result totaling portion 300 totals the digital watermark detected result y(k(i), m, j) for each category index k, each digital watermark strength index m, and each attack parameter index j and calculates a mean value r(k, m, j) as a detection ratio, and outputs the detection ratio r(k, m, j) to the robustness evaluation value calculating portion 2301.
The robustness evaluation value calculating portion 2301 calculates an attack robustness evaluation value V(k, m) based on the detection ratio r(k, m, j) that is received from the detected result totaling portion 300 and outputs the attack robustness evaluation value V(k, m) to the data combining portion 2303. The operation of the robustness evaluation value calculating portion 2301 will be described later.
On the other hand, the image quality deterioration amount d(i) is input to the image quality deterioration amount totaling portion 301. The image quality deterioration amount totaling portion 301 has a storing means. The image quality deterioration amount totaling portion 301 totals the image quality deterioration amount d(i) for each category index k and each digital watermark strength index m, calculates the mean value D(k, m) as an image quality deterioration ratio, and outputs the calculated mean value D(k, m) to the data combining portion 2302.
The data combining portion 2302 combines the robustness evaluation value V(k, m) that is received from the robustness evaluation value calculating portion 2301, the image quality deterioration ratio D(k, m) that is received from the image quality deterioration amount totaling portion 301, and the digital watermark strength s(m) and generates and outputs a digital watermark characteristic table shown in FIG. 1 for each category index k. Next, the robustness evaluation value calculating method performed by the robustness evaluation value calculating portion 2301 shown in FIG. 3 will be described.
To calculate the robustness evaluation value, the variation of the detection ratio in the case that the attack parameter x is successively varied is considered. The robustness evaluation value V(k, m) is given by the following formula.
V(k, m)=∫∞xe2x88x92∞w(x)r(k, m, x)dx xe2x80x83xe2x80x83(4) 
where k is a category index; m is a digital watermark strength index; x is an attack parameter; r(k, m, x) is a detection ratio that is a function of the attack parameter x when the digital watermark strength index is m; and W(X) is a weighting function.
The weighting function W(X) determines the degree of contribution of the detection ratio at each attack parameter x to the robustness evaluation value V(k, m). When the weighting function is properly set, the user""s sense against the deterioration due to an attack and attack frequency information can be affected to the evaluation value. In reality, the detection ratio against the digitized value x(j) is obtained rather than the detecting ratio against any attack parameter x. Thus, the robustness evaluation value V(k, m) is calculated by digitizing and approximating the formula (4).
Alternatively, the robustness evaluation value V(k, m) can be obtained corresponding to the following formula.                               V          ⁢                      xe2x80x83                    ⁢                      (                          k              ,              m                        )                          =                              1            L                    ⁢                      xe2x80x83                    ⁢                                    ∫                              -                ∞                            ∞                        ⁢                          T              ⁢                              xe2x80x83                            ⁢                              (                                                      r                    ⁢                                          xe2x80x83                                        ⁢                                          (                                              k                        ,                        m                        ,                        x                                            )                                                        ,                  α                                )                            ⁢                              xe2x80x83                            ⁢                              ⅆ                x                                                                        (        5        )            
where k is a category index; m is a digital watermark strength index; V(k, m) is a robustness evaluation value V(k, m); and L is a reference interval length of the attack parameter. T(x, xcex1) is a thresholding function given by the following formula.                               T          ⁢                      xe2x80x83                    ⁢                      (                          x              ,              a                        )                          =                  {                                                    1                                                              (                                      x                     greater than                     α                                    )                                                                                    0                                                              (                                      x                    ≤                    α                                    )                                                                                        (        6        )            
However, the second related art reference has the following problems.
As a first problem, it is difficult for the user to customize an attack robustness evaluation value calculating method. Although it is preferred for the user to freely designate a weighting function and a threshold value for calculating a robustness evaluation value, the digital watermark inserting system of the second related art reference uses a pre-calculated robustness evaluation value as an attack robustness evaluation value, it is difficult to tune the robustness evaluation value calculating method.
As a second problem, when a robustness evaluation value for a combination of a plurality of attacks is used for calculating the optimum digital watermark strength, the data amount to be stored adversely increases. Thus, it is necessary to reduce the data amount. In other words, according to the second related art reference, since all robustness evaluation values corresponding to combinations of a plurality of attacks should be stored, a huge amount of storage capacity is required. However, it is difficult to satisfy such a huge storage capacity.
An object of the present invention is to provide a digital watermark inserting system that allows the optimum digital watermark strength to be automatically calculated corresponding to a robustness evaluation value against an attack and an image quality deterioration ratio.
A first aspect of the present invention is a digital watermark inserting system for inserting digital watermark information into an input image, comprising a means for calculating a feature amount of the input image, categorizing the input image, and outputting a category index as the categorized result, a digital watermark characteristic calculating means for calculating an image deteriorating ratio and a robustness evaluation value against a digital watermark strength based on a robustness evaluation value calculation parameter and the category index, the robustness evaluation value calculation parameter being input by the user, a digital watermark strength calculating means for outputting the digital watermark strength to the digital watermark characteristic calculating means, deciding the optimum digital watermark strength based on digital watermark strength restriction information that is input by the user, and outputting the optimum digital watermark strength, and a digital watermark inserting means for converting input embedding data into digital watermark information, inserting the digital watermark information into the input image with an input parameter of the optimum digital watermark strength, and outputting the resultant image as a digital watermark inserted image.
A second aspect of the present invention is a digital watermark characteristic parameter table generating method for inserting digital watermark information into an input image, comprising the steps of calculating a feature amount of the input image, categorizing the input image with the calculated result, and outputting a category index as the categorized result, converting input embedding information into the digital watermark information, inserting the digital watermark information into the input image with input digital watermark strength, and generating a digital watermark inserted image as the inserted data, adjusting the strength of an attack with an input attack parameter, attacking the digital watermark inserted image with the adjusted attack strength, generating a resultant attacked image, detecting a digital watermark from the attacked image, outputting the detected result, comparing the input image with the digital watermark inserted image, calculating an image quality deterioration amount caused by the inserted digital watermark, and outputting the calculated the input quality deterioration ratio amount, and receiving the detected result of the digital watermark, the digital watermark strength, the attack parameter, the image quality deterioration amount, and the category index, totaling the detected results for each of combinations of the category index, the digital watermark strength, and the attack parameter, obtaining a detection ratio as the totaled result, totaling the image quality deterioration amount for each of combinations of the category index and the digital watermark strength, obtaining an image quality deterioration ratio as the totaled result, and calculating a digital watermark characteristic parameter table by using the detection ratio and the image quality deterioration ratio, and outputting the digital watermark characteristic parameter table.
A third aspect of the present invention is a record medium from which a computer reads a program that causes the computer to drive a digital watermark inserting system for inserting digital watermark information into an input image, the system comprising a means for calculating a feature amount of the input image, categorizing the input image, and outputting a category index as the categorized result, a digital watermark characteristic calculating means for calculating an image deteriorating ratio and a robustness evaluation value corresponding to a digital watermark strength based on a robustness evaluation value calculation parameter and the category index, the robustness evaluation value calculation parameter being input by the user, a digital watermark strength calculating means for outputting the digital watermark strength to the digital watermark characteristic calculating means, deciding the optimum digital watermark strength based on digital watermark strength restriction information that is input by the user, and outputting the optimum digital watermark strength, and a digital watermark inserting means for converting input embedding data into digital watermark information, inserting the digital watermark information into the input image with an input parameter of the optimum digital watermark strength, and outputting the resultant image as a digital watermark inserted image.
A fourth aspect of the present invention is a record medium from which a computer reads a program that causes the computer to perform a method for inserting digital watermark information into an input image, the method comprising the steps of (a) calculating a feature amount of the input image, categorizing the input image, and outputting a category index as the categorized result, (b) digital watermark characteristic calculating means for calculating an image deteriorating ratio and a robustness evaluation value corresponding to a digital watermark strength based on a robustness evaluation value calculation parameter and the category index, the robustness evaluation value calculation parameter being input by the user, (c) digital watermark strength calculating means for outputting the digital watermark strength to step (b), deciding the optimum digital watermark strength based on digital watermark strength restriction information that is input by the user, and outputting the optimum digital watermark strength, and (d) digital watermark inserting means for converting input embedding data into digital watermark information, inserting the digital watermark information into the input image with an input parameter of the optimum digital watermark strength, and outputting the resultant image as a digital watermark inserted image.
Next, with reference to the accompanying drawings, the present invention will be described. A digital watermark inserting system according to the present invention comprises a means (103, FIG. 4) for calculating a feature amount of the input image, categorizing the input image, and outputting a category index as the categorized result, a digital watermark characteristic calculating means (104, FIG. 4) for calculating an image deteriorating ratio and a robustness evaluation value corresponding to a digital watermark strength based on a robustness evaluation value calculation parameter and the category index, the robustness evaluation value calculation parameter being input by the user, a digital watermark strength calculating means (100, FIG. 4) for outputting the digital watermark strength to the digital watermark characteristic calculating means (104, FIG. 4), deciding the optimum digital watermark strength based on digital watermark strength restriction information that is input by the user, and outputting the optimum digital watermark strength, and a digital watermark inserting means (102, FIG. 4) for converting input embedding data into digital watermark information, inserting the digital watermark information into the input image with an input parameter of the optimum digital watermark strength, and outputting the resultant input as a digital watermark inserted image.
In the digital watermark inserting system according to the present invention, the digital watermark characteristic calculating means (104, FIG. 4) has a first storing means (101, FIG. 5) for storing a digital watermark characteristic parameter table for each of various category indexes, the digital watermark characteristic parameter table describing the relation of a digital watermark strength, an image detection ratio, and a detection ratio parameter, the detection ratio parameter describing a detection ratio curve/curved surface that approximates the variation of the detection ratio of the digital watermark information against an attack parameter, selecting a detection ratio characteristic parameter table corresponding to the category index, and outputting the image quality deterioration ratio and the detection ratio characteristic parameter corresponding to the digital watermark strength that is output from the digital watermark strength calculating means (100, FIG. 4), and a robustness evaluation value calculating means (105, FIG. 5) for obtaining the detection ratio curve/curved surface with the detection ratio characteristic parameter, performing a statistic process based on the robustness evaluation value calculation parameter that is input by the user, calculating the robustness evaluation value, and outputting the robustness evaluation value. In the digital watermark inserting system according to the present invention, the digital watermark characteristic calculating means (104, FIG. 4) has a second storing means (171, FIG. 6) for storing a digital watermark characteristic parameter table describing the relation of a category index, an image quality deterioration ratio curve parameter describing an image quality deterioration ratio curve that approximates the variation of the image quality deterioration ratio against a digital watermark strength, and a detection ratio characteristic general parameter that describes a detection ratio characteristic parameter curve approximating the variation of a detection ratio characteristic parameter against the digital watermark strength and outputting an image quality deterioration ratio curve parameter and a detection ratio characteristic general parameter corresponding to the category index, an image quality deterioration ratio calculating means (100, FIG. 4) for obtaining an image quality deterioration ratio curve with the image quality deterioration ratio curve parameter, calculating the image quality deterioration ratio corresponding to the digital watermark strength that is output from the digital watermark strength calculating portion, and outputting the calculating image quality deterioration ratio, and a robustness evaluation value calculating means (173, FIG. 6) for obtaining the detection ratio characteristic parameter curve with the detection ratio characteristic general parameter, calculating a detection ratio characteristic parameter corresponding to the digital watermark strength that is output from the digital watermark strength calculating portion, obtaining the detection ratio curve/curved surface with the calculated detection ratio characteristic parameter, performing a statistic process based on the robustness evaluation value calculation parameter that is input by the user, and outputting the calculated robustness evaluation value as the processed result.
In the digital watermark inserting system according to the present invention, the robustness evaluation value calculating means (105, FIG. 5 or 173, FIG. 6) obtains an inner product of the detection ratio curve and a weighting function so as to calculate the robustness evaluation value.
In the digital watermark inserting system according to the present invention, the robustness evaluation value calculating means (105, FIG. 5 or 173, FIG. 6) obtains a region of an attack parameter of which a detection ratio exceeds a predetermined threshold value with the detection ratio curve and calculates the robustness evaluation value based on the length of the region.
In the digital watermark inserting system according to the present invention, the detection ratio characteristic parameter is a detection ratio curve parameter that represents the detection ratio curve for a single attack.
In the digital watermark inserting system according to the present invention, the detection ratio characteristic parameter is composed of the detection ration curve parameter for a single attack and an attack correlation curved surface parameter that is a parameter that describes an attack correlation curved surface approximating an attack correlation value defined based on the ratio of the product of detection ratios of single attacks and a detection ratio for a complex attack, and the robustness evaluation value calculating means (105, FIG. 5) obtains the detection ratio curve for a single attack composing a complex attack with the detection ratio curve parameter for the single attack, obtains an attack correlation curved surface with the attack correlation curved surface parameter, obtains the detection ratio curved surface for the complex attack based on the product of the detection ratio curve for the single attack and the attack correlation curved surface, and calculates the robustness evaluation value.
In the digital watermark inserting system according to the present invention, the detection ratio general parameter is a detection ratio curve general parameter that represents a curve approximating the variation of the detection ratio curve parameter against a digital watermark strength for a single attack. In the digital watermark inserting system according to the present invention, the detection ratio characteristic general parameter is composed of a detection ratio curve general parameter for a single attack and an attack correlation curved surface general parameter that represents a curve approximating the variation of an attack correlation curve parameter against the digital watermark strength. The robustness evaluation value calculating means (173, FIG. 6) obtains the detection ratio curve for a single attack composing a complex attack with a detection ratio curve general parameter for the single attack, obtains an attack correlation curved surface with the attack correlation curved surface general parameter, obtains the detection ratio curved surface for the complex attack based on the product of the detection ratio curve for the single attacks and the attack correlation curved surface, and calculates the robustness evaluation value.
In the digital watermark inserting system according to the present invention, the attack correlation curved surface and the weighting function for a complex attack are a linear sum of a function separable for an attack parameter of each attack.
In the digital watermark inserting system according to the present invention, the restriction information of the digital watermark strength is an allowable limit value of the image quality deterioration ratio. The digital watermark strength calculating means decides the optimum digital watermark strength in the allowable limit value of the image quality deterioration ratio and outputs the decided optimum digital watermark strength.
In the digital watermark inserting system according to the present invention, the restriction information of the digital watermark strength is a limit value of a safety index against an attack. The digital watermark strength calculating means decides the optimum digital watermark strength in a range of which the robustness evaluation value against the attack exceeds the limit value of the safety index and outputs the decided optimum digital watermark strength.
In the digital watermark inserting system according to the present invention, the restriction information of the digital watermark is a weighting index that defines the balance of the image quality deterioration amount and the safety index. The digital watermark strength calculating means decides the ratio of the contribution of the image quality deterioration amount and the safety index for deciding the optimum digital watermark strength with the weighting index.
In the digital watermark inserting system according to the present invention, the digital watermark characteristic means (131, FIG. 7) has a digital watermark characteristic parameter table generating means (132, FIG. 7) for generating the digital watermark characteristic parameter table that is input to the digital watermark characteristic calculating means (131, FIG. 7).
In the digital watermark inserting system according to the present invention, the digital watermark characteristic parameter table generating means (132, FIG. 7) has a digital watermark inserting means (200, FIG. 12) for converting input embedding information into digital watermark information, inserting the digital watermark information into the input image with the input digital watermark strength, and generating the digital watermark inserted image, an attack image generating means (201, FIG. 12) for adjusting the strength of an attack with an input attack parameter against the digital watermark inserted image, and generating an attacked image, a digital watermark detecting menas (202, FIG. 12) for detecting a digital watermark from the attacked image and outputting the detected result, an image quality deterioration amount calculating means (203, FIG. 12) for comparing the input image with the digital watermark inserted image, calculating an image quality deterioration amount caused by the inserted digital watermark with the compared result, and outputting the calculated image quality deterioration amount, a categorizing means (204, FIG. 12) for calculating a feature amount of the input image, categorizing the input image with the calculated feature amount, and outputting a category index corresponding to the categorized result, and a digital watermark characteristic parameter table calculating means (205, FIG. 12) for receiving the detected result of the digital watermark, the digital watermark strength, the attack parameter, the image quality deterioration amount, and the category index, totaling the detected results of each of combinations of the category index, the digital watermark strength, and the attack parameter, obtaining a detection ratio as the totaled result, totaling an image quality deterioration amount of each of combinations of the category index and the digital watermark strength, obtaining a image quality deterioration ratio as the totaled result, calculating a digital watermark characteristic parameter table using the detection ratio and the image quality deterioration ratio, and outputting the calculated digital watermark characteristic parameter table.
In the digital watermark inserting system according to the present invention, the digital watermark characteristic parameter table calculating means has a detection ratio calculating means (300, FIG. 13) for totaling a detected result of the digital watermark information for each of the attack parameter, the digital watermark strength, and the category index, calculating detection ratio data with the totaled result, and outputting the calculated detection ratio data, an image quality deterioration ratio calculating means (301, FIG. 13) for totaling an image quality deterioration amount for each of the category index and the digital watermark strength and outputting the resultant statistic amount as an image quality deterioration ratio, a digital watermark characteristic extracting means (302, FIG. 13) for calculating detection ratio descriptive information describing the variation of the detection ratio data against the digital watermark strength, the attack parameter, and the category index and image quality deterioration ratio descriptive information describing the variation of the image quality deterioration ratio and outputting the detection ratio descriptive information and the image quality deterioration ratio descriptive information, and a data combining means (303, FIG. 13) for combining the digital watermark strength, the category index, the image quality deterioration ratio descriptive information, and the detection ratio descriptive information, generating a digital watermark characteristic parameter table as the combined result, and outputting the generated digital watermark characteristic parameter table.
In the digital watermark inserting system according to the present invention, the digital watermark characteristic extracting means has a detection ratio characteristic extracting means (320, FIG. 14) for approximating a function representing the variation of the detection ratio data against the attack parameter for each of the category index and the digital watermark strength with a curve/curved surface, calculating a detection ratio characteristic parameter describing the curve/curved surface, and outputting the calculated detection ratio characteristic parameter as the detection ration descriptive information. The image quality deterioration ratio is output as the image quality deterioration ratio descriptive information.
In the digital watermark inserting system according to the present invention, the detection ratio characteristic parameter calculated by the detection ratio characteristic extracting means (320, FIG. 14) is a detection ratio curve parameter for a single attack.
In the digital watermark inserting system according to the present invention, the detection ratio characteristic parameter calculated by the detection ratio characteristic extracting means (320, FIG. 14) is composed of a detection ratio curve parameter for a single attack and an attack correlation curved surface parameter describing the correlation of single attacks.
In the digital watermark inserting system according to the present invention, the digital watermark characteristic extracting means (302, FIG. 13) has a detection ratio characteristic calculating means (340, FIG. 15) for approximating a function that represents the variation of the detection ratio data against the attack parameter for each of the category index and the digital watermark strength with a curve/curved surface, calculating a detection ratio characteristic parameter that represents the curve/curved surface, approximating the variation of the detection ratio characteristic parameter against the digital watermark strength with a curve, obtaining a detection ratio characteristic general parameter that describes the curve, and outputting the detection ratio characteristic general parameter as the detection ratio descriptive information, and an image quality deterioration ratio characteristic extracting means (341, FIG. 15) for approximating the variation of the image quality deterioration ratio against the digital watermark strength with a curve, calculating an image quality deterioration ratio curve parameter that describes the curve, and outputting the image quality deterioration ratio curve parameter as the image quality deterioration ratio descriptive information.
In the digital watermark inserting system according to the present invention, the detection ratio characteristic parameter and the calculated detection ratio characteristic general parameter calculated by the detection ratio characteristic calculating means (340, FIG. 15) are a detection ratio curve parameter for a single attack and a detection ratio curve general parameter for a single attack, respectively.
In the digital watermark inserting system according to the present invention, the detection ratio characteristic parameter calculated by the detection ratio characteristic calculating means (340, FIG. 15) is composed of a detection ratio curve parameter for a single attack and an attack correlation curved surface parameter that describes the correlation of single attacks. The detection ratio characteristic general parameter calculated by the detection ratio characteristic calculating means (340, FIG. 15) is composed of a detection ratio curve general parameter for a single parameter and an attack correlation cured surface general parameter.